No lighting is working at all
You set the "Clamp Direct and Clamp Indirect" to a very small number.



Here is a screenshot with,

Clamp Direct = 1, Clamp Indirect = 10, Sun lamp strength = 2.

The documentation for these settings is here https://docs.blender.org/manual/en/dev/render/cycles/settings/scene/render/integrator.html



Clamp direct will make all light values larger than the set value be ignored (or clamped), so if you set clamp at 0.03 for example, all light values will be considered up to 0.03, even if your light is brighter than brightest star in the universe.